Objectives: 1. We will continue our studies of Leydig cell carcinogenesis paying particular attention to the effects of estrogens on DNA and RNA metabolism. 2. We wish to study tumor regression employing hormone dependent transplanted Leydig cell tumors. 3. We will study pituitary adenoma production in much the same way as we are pursuing the Leydig cell tumor problem. 4. We will study neovascularization employing transplanted mouse testes. 5. We will explore the effects of adrenal cortical hormones upon mammary tumorigenesis in mice.